Modern navigation devices (including smart phones and tablet PCs) calculate routes between geographic positions, like a route start position, route end point and optional intermediate positions. Based on the geographic positions and on provided digitized map data, the navigation devices calculate and output to the user a recommended route. In addition, navigation devices comprise route guidance functionalities designed to output appropriate maneuver instructions for upcoming maneuvers when travelling along the pre-calculated route. Instructions or warnings comprising information on speed limits, allowed travel directions (one-way or both directions), potential traffic congestions, existence of roadworks, etc. may be also output. Other information may be directed to upcoming points of interest, or POIs. All this information is based on digitized map data usually stored in a storage unit of the navigation device or provided online by a map data supplier.
In many situations, the user does not need route calculation or route guidance to a repeatedly visited destination, since the user knows every detail of the route to be travelled. Examples for such routes are, for instance, the daily way to work, the return to home, the way to frequently visited friends or clients, the way to the next supermarket or to the airport, and so on. For such frequently travelled routes the user generally knows dangerous route passages, the position of traffic lights and speed limitation signs, dangerous curves and junctions, the detailed characteristic of the junctions to be taken and how to turn on the junctions etc. For this reason, the user does not desire route guidance and, consequently, the user does not enter destination information, so that no route guidance is active.
On the other hand, road networks are continuously subjected to changes. For instance, road specific rules, like speed limits, the direction of one-way streets, the right of way or other accessibility condition are frequently changed. In other cases roadworks are set up or are terminated, the geometry of route segments or junctions has been changed or POIs associated with roads have been newly installed or closed. Nowadays such modification can be efficiently encountered by frequently updating the map database of the navigation device. For instance, navigation database formats, like the Navigation Data Standard, or NDS, format provide incremental database updates, in which small data portions rather than the whole database can be individually updated. In NDS an incremental update of map data on tile-basis (a tile represents a local geographic area of predetermined dimensions) is supported. As such, it can be expected that changes (even temporary changes) in the road network are quickly recorded and incorporated in the data set so that route guidance and route calculation are substantially performed on up-to-date navigation data.
However, in case the user is driving a frequently travelled road without route guidance support, the user will not be informed by the navigation device on possible changes. The user will also not immediately notice performed changes on the travelled route. In addition, since the user is readily familiar with the route, the user often does not drive as carefully as he or she drives on unknown routes. Thus, also minor changes, such as the installation of an additional traffic light or of a speed limit sign, might surprise the driver and might lead to dangerous situations (for instance, when the driver is performing an abrupt brake maneuver), since the user does not expect such changes when travelling along the route.